The present invention relates to fire and explosion prevention systems.
Many systems are known on the market and have been proposed for fighting fires. Such systems employ thermal, light, heat or pressure detectors to determine the existence of a fire or explosion and to actuate fire extinguishing units and are known to be effective for suppressing fires of various origins.
There is no system presently on the market capable of effectively suppressing incipient explosions from both high energy and low energy ignitions. In order to effectively suppress an explosion such as that arising when a HEAT (High Energy Anti Tank) round strikes an armored vehicle, it is necessary to achieve suppression within approximately 100 msecs. following the onset thereof. If suppression can be achieved in this time frame, skin burns to exposed personnel can be limited to first degree and the pressure build-up can be limited to one atmosphere.
The present invention also relates to detectors for automatically sensing the presence of a dangerous condition and energizing appropriate protective apparatus. Many types of detectors are known for sensing various dangers or potentially dangerous conditions. Pressure and temperature detectors are well known as are optical flame and smoke detectors. Fire detection by sensing emitted ultraviolet radiation is also well known.
In the design of such detectors and more particularly in the design of explosion detectors, two conflicting design criteria operate. The first is minimalization of the reaction time in which an output indication signal can be provided to protective apparatus and second is reliability in the presentation of false alarms. Particularly with respect to explosion protection the short reaction time is critical since remedial measures against most types of explosion must be taken within approximately 100 msec on the onset thereof in order to prevent serious damage to life and property. Reliability is also critical since such explosion detectors are often coupled to automatic explosion prevention apparatus and it is extremely desirable that each apparatus not be operated except in the case of actual need.
A number of fire and explosion detection systems have been proposed.
Two relevant examples are illustrated in U.S. Pat. Nos. 3,825,754 and 3,931,521. U.S. Pat. No. 3,931,521 describes a dual spectrum infrared fire detector which is activated by the coincident receipt of radiant energy in 7-30 micron spectral band and in 0.7-1.2 micron spectral band. The long wave length spectral band is detected by using a thermal detector such as a thermopile. The detector system described in U.S. Pat. No. 3,931,521 suffers from the disadvantage that the short wave length detector is responsive to light in the visible band which is transmitted through the atmosphere, and the long wavelength detector operates in a region of relatively high noise. Thus, the device operates at a relatively low sensitivity threshold of operation.
U.S. Pat. No. 3,825,754 describes a dual spectrum infrared fire detector similar to that described in U.S. Pat. NO. 3,931,521 and also comprises a three channel infrared radiation detection system for distinguishing between large explosive fires and large explosions which cause no fire. The system described in U.S. Pat. No. 3,825,754 shares the disadvantages of the system described in U.S. Pat. No. 3,931,521, as discussed hereinabove.
U.S. Pat. No. 3,665,440 shows a combination ultraviolet and infrared detection system which provides an output only in the absence of ultraviolet radiation during the receipt of infrared radiation. Such a detector system is not suitable for use in detecting incipient explosions.
U.S. Pat. No. 3,653,016 shows a combination infrared light detector and ultraviolet light detector coacting as a fire discrimination system. Since visible light is detected the false alarm rate of such a detector is increased when visible light is present in the detection environment.